7. Project Summary/Abstract Astrocytes are vital to brain metabolism and help to optimize synaptic function and promote neuronal health. Direct coupling of astrocytes to the extracellular milieu via unapposed hemichannels (uHCs)?made up of connexin 43 (Cx43) proteins?appears to be increased under a variety of pathological conditions. Elevated levels of amyloid-? (A?) peptides and pro-inflammatory cytokines, characteristic of Alzheimer?s disease (AD), lead to greater uHC permeability?which, in turn, impairs neuronal function and viability. In this project, we will test the novel hypothesis that A?-dependent changes in uHCs are mediated, in part, by aberrant activation of the protein phosphatase calcineurin (CN), shown by our lab and others to drive several critical components of the activated astrocyte phenotype. Aim 1 will use a combination of adenoviral vectors and pharmacological agents, in addition to Western blot, ethidium bromide uptake, patch-clamp electrophysiology, and a variety of biochemical assays, to determine whether CN and Cx43 are necessary and sufficient for the effects of A? on the functional status of HCs in primary astrocytes. In addition, this aim will determine the feasibility of using a novel peptide-based reagent, 43Gap52, to selectively disrupt CN/Cx43 interactions without inhibiting CN activity per se. This aim will establish whether aberrant CN/Cx43 interactions in astrocytes are a direct outcome of A? pathology. Aim 2 will use adeno-associated virus (AAV) bearing astrocyte-specific promoters and CN activators (active CN fragment) or CN inhibitors (CN-autoinhibitory peptide or 43Gap52) to selectively modulate astrocytic CN/Cx43 interactions in an intact mouse model of AD. The functional status of astrocytic uHCs will be investigated in acutely prepared brain slices using an EtBr uptake assay, as described for Aim 1. In addition, slice electrophysiology will be used to assess the impact of CN/Cx43 interactions on hippocampal synaptic strength and plasticity. This Aim will validate Aim 1 results in a commonly used animal model of AD, en route to determining the extent to which CN/Cx43 interactions in astrocytes disrupt synaptic function during the progression of A? pathology. These studies will shed light on the role of astrocytic HCs in AD pathophysiology and determine whether disruption of the CN/Cx43 interaction is a feasible strategy for ameliorating neurologic dysfunction due to AD and other types of neurodegenerative disease.